Myth: Eating Soya Increases Breast Cancer Risk

Myth: Eating Soya Increases Breast Cancer Risk

In this article, we look at the known causes of Breast Cancer, and look to disprove the myths that eating soya foods increase the risk of breast cancer.

Breast Cancer

Breast cancer starts when cells in the breast begin to grow out of control. These cells usually form a tumour that can often be seen on an x-ray or felt as a lump. The tumour is malignant (cancer) if the cells can invade surrounding tissues or spread (metastasize) to distant areas of the body. Breast cancer occurs almost entirely in women, but men can get breast cancer, too.

Cells in nearly any part of the body can become cancerous and can spread to other areas of the body.

Where Breast Cancer Starts

Breast cancers can start from different parts of the breast. Most breast cancers begin in the ducts that carry milk to the nipple (ductal cancers). Some start in the glands that make breast milk (lobular cancers). There are also other types of breast cancer that are less common.  A small number of cancers start in other tissues in the breast. These cancers are called sarcomas and lymphomas and are not really thought of as breast cancers.

Although many types of breast cancer can cause a lump in the breast, not all do. There are other symptoms of breast cancer one should watch out for and report to a health care provider.

It’s also important to understand that most breast lumps are not cancer, they are benign.

Benign breast tumours are abnormal growths, but they do not spread outside of the breast and they are not life threatening. But some benign breast lumps can increase a woman’s risk of getting breast cancer. Any breast lump or change needs to be checked by a health care provider to determine whether it is benign or cancer and whether it might impact your future cancer risk. 

Known Causes

Although there is a lot known about the risk factors for breast cancer, many women at high risk for it do not get breast cancer, and others with no known risk factors can get breast cancer.

Among the most significant factors are advancing age and a family history of breast cancer. Risk increases for a woman who has certain types of benign breast lumps and increases significantly for a woman who has previously had cancer of the breast or the ovaries.

A woman whose mother, sister, or daughter has had breast cancer is two to three times more likely to develop the disease, particularly if more than one first-degree relative has been affected. Researchers have identified two genes responsible for some instances of familial breast cancer. These genes are known as BRCA1 and BRCA2. About one woman in 200 carries the genes. Having one of them predisposes a woman to breast cancer but does not ensure that she will get it.

Generally, women over age 50 are more likely to get breast cancer than younger women.

Soy Myths and Facts:

MYTH:  All Soy Foods Raise Your Risk for Breast Cancer

FACT:    *Phytoestrogens found in soya have often been blamed for being a cause of breast cancer. These plant-based chemicals are similar in structure to oestrogen. Most breast cancers are sensitive to oestrogen or,  are “oestrogen-receptor-positive”  meaning that oestrogen fuels their growth. Thus a wide-spread fear was created that soy could act as oestrogen in the body and stimulate cancer cells.

Yet a steady stream of recent studies show that a diet high in soy did not increase the chances of developing breast cancer and may even reduce that risk.

In one specific study of more than 73,000 Chinese women, researchers found that those who ate at least 13 grams of soy protein a day, roughly one to two servings, were 11% less likely to develop breast cancer than those who got less than 5 grams.

It has also been shown that in Asian cultures, where people eat a lot of soy from a young age, there are lower rates of breast cancer. In Asian cultures most people eat soy in its traditional and many various forms.

A meta-analysis done in 2005 also showed that those who consumed the most soy isoflavones — about the amount in a serving of tofu OR 50g soya porridge + 200ml soya milk – were 29% less likely to get the disease compared to those who consumed the least.

MYTH:  If You Have or Had Breast Cancer Avoid All Soy Foods

FACT:    The science shows that, just as eating a moderate amount of whole soy doesn’t make you more likely to get breast cancer, it also doesn’t seem to raise your risk for recurrence.

In one report, researchers analyzed data from diet surveys completed by more than 9,500 American and Chinese women. Those who said they ate the most soy were 25% less likely to have their cancer return compared to those who had the least.

Some experts worried that soy might interfere with breast cancer drugs that lower oestrogen levels, such as tamoxifen. But the same study showed that soy also protected against recurrence in patients who took tamoxifen.

The soy foods that the study included were tofu, soy milk, and fresh soybeans. As expected, the Chinese women ate far more of it than those in the U.S. The results still held when the researchers considered that fact.

Understanding Soya and Phyoestrogens


Phytoestrogens are plant compounds that can improve oestrogen metabolism through a variety of mechanisms, and are currently being extensively investigated as a potential alternative therapy for a range of conditions associated with oestrogen imbalance (including menopausal symptoms, PMS, endometriosis, prevention of breast and prostate cancer, and protection against cardiovascular disease and osteoporosis.

There are 2 types of phytoestrogens: ISOFLAVONES and LIGNANS.

  1. Isoflavones

Found in Soy (most common food source of isoflavones), legumes, alfalfa, clover, licorice root and kudzu root.

Higher intakes of soy isoflavones (as is found in traditional Japanese diets) is associated with low rates of hormone-dependant cancers.    THE AVERAGE DAILY ISOFLAVONE INTAKE OF JAPANESE WOMEN is 20-80mg; WHILE THAT OF AMERICAN WOMEN is 1-3mg.

Soy Isoflavones are antioxidants, and are the active components in the soy bean accounting for +/- 75% of the beneficial effects of soy-based foods in human health.

Soy isoflavones have many important functions, one being:

When oestrogen levels are high, isoflavones block the more potent forms of oestrogen produced by the body. In this way they may help to prevent hormone-driven diseases, such as breast and prostate cancer.

In conclusion:

It can be safely stated that whole soy foods, incorporated into an overall balanced diet, can improve women’s health, and, as per recent findings are considered safe when considering breast cancer risk.

Examples of sources of Soy:

Soya Life Porridge

Soya Life Instant Meal Replacement Drink


REFERENCES: on request.

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